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Volcanic activity

Volcanic activity. Classification of igneous rocks. Distribution of main volcanoes. Fujiyama, Japan. Mount St. Helen before May 18, 1980. Mount St. Helen after 1980. 400 km 2 of devastated area. Trees 25 km away from Mt. St Helen. Gases at 800 °, Mount St. Helen eruption.

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Volcanic activity

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  1. Volcanic activity

  2. Classification of igneous rocks

  3. Distribution of main volcanoes

  4. Fujiyama, Japan

  5. Mount St. Helen before May 18, 1980

  6. Mount St. Helen after 1980

  7. 400 km2 of devastated area. Trees 25 km away from Mt. St Helen

  8. Gases at 800°, Mount St. Helen eruption

  9. Succession of events

  10. Violent or “gentle” eruptions? Magma composition is the main factor

  11. Fluid basaltic lava emitted from the flank eruption on Kalauea, Hawaii Velocity up to 30 km/h

  12. Slow moving aa flow

  13. Dissolved gases • Confining pressure • Volume increase with drop of confining pressure Basaltic magma fountains (generally harmless)

  14. Material extruded during an eruption • Lava flow • Gases • Pyroclastic material

  15. Pahoehoe (ropy) lava flow, Hawaii

  16. Viscose lava of intermediate to felsic composition “aa” type of flow Velocity 5-50 m/h

  17. Lava tubes

  18. Active lava tube and the collapse roof, Hawaii

  19. Eruption into water Pillow lavas

  20. Gases • Gases constitute 1-6% of total erupted material but is thousand of tons per day Hawaiian eruptions: - 70% water vapor - 15% carbon dioxide - 5% nitrogen - 5% sulfur - Rest is chlorine, hydrogen, argon

  21. Pyroclastic rocks or pyroclastics are clastic rocks composed solely or primarily of volcanic materials. Pumice deposits

  22. Classification of pyroclastic rocks

  23. Volcanic bombs Bombs ejected as incandescent lava; solidify in air

  24. Tuff and volcanic blocks, Pektusan (China/Korea border)

  25. Volcanoes (terms) • Crater (D < 1 km) • Caldera (D > 1 km) • Vent – pipeline connecting with magmatic chamber • Parasitic cone • Fumaroles – emit only gases

  26. Summit caldera of Mauna Loa, Hawaii

  27. Summit caldera of Pektusan

  28. Shield volcanoes are built primary of fluid basalts lava flows

  29. Mauna Loa - shield volcano in Hawaii Largest in the world. Its total height is 9 km 170 m.

  30. Lava flows meet the sea (Hawaii)

  31. Mauna Loa

  32. Cinder cones

  33. Cinder cones Cinder cones and craters in Arizona

  34. Composite cones or stratovolcano

  35. Composite cones or stratovolcano • Most violent type of volcanic activity • Pompeii 79 A.D. is example

  36. Mount Pelée

  37. Mt Pelée, Martinique, 1902 • Eruption of Mt Pelée • Nueeardente (glowing avalanches) • travelled 6 km at 33m/s (approx. 200 km/h) • temperature: 700 degrees C • Destroyed town of St Pierre • Killed 28,000 people in 3 minutes • 2 survivors in St Pierre

  38. St. Pierre after the eruption of Mount Pelee

  39. NueeardenteMount St. Helens

  40. Lahar of stratovolcano eruptions • Volcanic ash and debris saturated with water • Move 30 km per hour

  41. 2 Mechanism of caldera formation

  42. Caldera Crater Lake in Oregon

  43. Volcanic domes

  44. Continent of Atlantis • Collapse of Minoan civilization 1500 B.C. • Caldera 14 km across

  45. Volcanic necks • Formed due to erosion • Pyroclastic rocks are weak • Vent rocks are resistant to erosion

  46. Fissure eruptions

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